1. Field of the Invention
The present invention relates to graphical images and, more particularly, to condensing graphical images that are animated.
2. Description of the Related Art
Graphic images are often stored as image files in a variety of different formats. Often these formats contain some sort of compression to keep the size of the image files manageable. For example, JPEG compression or wavelet compression are currently popular compression techniques for image files.
To provide the appearance of animation on a display screen of a computer system, a series of images can be sequentially displayed. One format for graphical images that supports animation is GIF89a, which pertains to Graphics Interchange Format (GIF), version 89a, by Compuserve Incorporated, Columbus, Ohio. Since animations typically include a relatively large number of images to be sequentially displayed, the image files storing the animated images often use compression. The GIF89a format, for example, does utilize compression.
One problem with animated image files is that even with compression the file sizes are still large. These large files not only require a large amount of storage space, but also make the transmission of these files from one computer to another time consuming. With the development of the Internet and the frequency with which animated images are provided on World Wide Web (WWW) pages, there is an ever increasing need to improve the transmission time of animated image files.
Prior approaches have tried to re-compress image files to reduce their size. These require the computationally complex operations of decompression followed by re-compression. Although improvement in file size can be obtained, the computational requirements are often too burdensome. Additionally, prior approaches have sacrificed image quality (e.g., number of colors, resolution, size, etc.) in attempting to reduce image file size.
The storage and transmission difficulties associated with animated image files is particularly problematic in the case where a server system operates as a proxy system. A proxy system stores images relatively local to its requesters so that if the same images are again needed, they are readily available and can be rapidly forwarded to the appropriate requestor without the delay of having to first obtain the images from a content provider. Hence, in a server system desiring to store (e.g., cache) images for subsequent transmission to requesters, the large size of animated image files makes them difficult to handle.
Thus, there is a need for improved techniques for transmission and storage of animated image files.